How much noise is too much noise?

[oO Stevie Oo]

Evening

Im struggling with my ISO, My camera hates going above even ISO 400
I always try to shoot the lowest ISO possible but am I loosing detail doing that?
I usually go by ISO 100 for sunny daylight, 200 for cloudy but bright and 400 for 'looks like its gonna rain' and last light.

I thought this was pretty much ok but I keep seeing noise on pictures I wasnt expecting to see it on, mainly around ISO 400.

Also I am struggling to setup the flash for manual mode in the house etc, I normally go widest aperture and vary the shutter between 1/100 and 1/200, with the flash on TTL or 1/64 - 1/128, but again I'm struggling with the ISO in this area too.

So basically Im just looking for a few tips on what ISO margin to stay in and how to do flash photography correctly in manual as I'm just guessing at the moment

Any help appreciated
Cheers

 

[oO Stevie Oo]

Nikon D80 mate

 

[oO Stevie Oo]

Cheers all
A new body is in the pipeline,
Flash currently is the stock built in flash (weak I know)
I only shoot in RAW

I'll try the over exposing though and see if that helps

cheers